In general, a sensor-mounted terminal which includes a sensor such as a temperature sensor, a humidity sensor, or an air pressure sensor disposed therein and which has a communication function has been used. Using such a sensor-mounted terminal, a sensor value obtained by a sensor at a predetermined interval is transmitted to a center server connected to the sensor-mounted terminal through communication network. An administrator who manages the center server recognizes states of areas around such terminals in accordance with such sensor values supplied from the terminals.
As described above, since a sensor-mounted terminal uses electric power for operating sensors and electric power for executing communications, a considerably larger amount of electric power is consumed when compared with a communication terminal which does not include a sensor or a sensor which does not have a communication function.
In recent years, a technique of reducing power consumption of such a sensor-mounted terminal has been disclosed. For example, the following technique has been used: A portable terminal which operates using a battery is installed in a certain region such that a user can reach the terminal and another portable terminal is installed in another region such that the user may not reach the terminal. In this state, when output values of two sensors are equal to or smaller than a predetermined value per a predetermined period of time, the terminals enter a power-off mode in a general technique.